Continuing Education Activity
Indinavir is an alpha-amino acid amide protease inhibitor used as a treatment therapy for Human immunodeficiency virus (HIV) infections, potentially leading to acquired immunodeficiency syndrome (AIDS). This activity describes the use by the healthcare team, the indications, action, and contraindications for indinavir as a valuable agent in HIV therapy.
- Identify the mechanism of action of indinavir.
- Describe the potential adverse effects of indinavir.
- Outline the appropriate monitoring for a patient on therapy with indinavir.
- Review the interprofessional team strategies for improving care coordination and communication to advance indinavir and improve outcomes.
Indinavir is an alpha-amino acid amide protease inhibitor used as a treatment therapy for Human immunodeficiency virus (HIV) infections, which can lead to acquired immunodeficiency syndrome (AIDS). The FDA approved indinavir in 1996 as it was among the first HIV protease inhibitors authorized for use in the United States. Indinavir has been shown to decrease the likelihood of death as a result of AIDS progression.
For patients to obtain maximal benefit from the medication, indinavir is commonly combined with other HIV antiretroviral medications, such as the HIV protease inhibitor ritonavir. Indinavir is also subject to a high rate of mutation of the viral protease gene. Therefore an Indinavir monotherapy regime is rarely used to prevent the likelihood of drug resistance.
Indinavir metabolism occurs via hepatic cytochrome CYP450, specifically the subfamily CYP3A4, with 20% excreted through urine. Due to the high percentage of urine excretion of unaltered indinavir, a high risk of lithiasis exists.
Recent studies have analyzed the effects of indinavir as an anti-cancer agent.  Human papillomavirus is known to be induced by increased expression of eukaryotic translation initiation factor 4E (eIF4E), potentially leading to cervical cancer. Indinavir is an inhibitor of eIF4E. Therefore, recent research has examined its role as a possible cervical cancer treatment.
Mechanism of Action
Indinavir acts through a competitive inhibition mechanism. The medication binds the active catalytic site of HIV protease, thereby inhibiting the enzyme's ability to cleave polypeptides into active, infectious proteins. This inhibition, in turn, decreases the number of cleaved polypeptides in the blood, which therefore aids in reducing the amount of active HIV RNA in vivo.
Indinavir metabolism occurs through cytochrome CYP3A4. Therefore, patients currently taking medications that are also metabolized by CYP3A4 may cause an increase in the metabolism of Indinavir. Thus, since indinavir's concentration in a patient's bloodstream increases, its adverse effects will become exacerbated by increased drug clearance. This effect commonly occurs with herbal supplements such as St. John’s wort (Hypericum perforatum) and primarily occurs as a result of the activation of pregnane-X-receptor (PXR). On the contrary, if patients take indinavir with a medication that inhibits CYP3A4 activity, indinavir's clearance will decrease, which will cause elevated levels of indinavir in the bloodstream. Therefore, indinavir will be metabolized slower, potentially leading to reduced efficacy.
Patients on antiretroviral therapy (ART) have an increased risk for renal insufficiency. Indinavir is commonly known for causing lithiasis, specifically nephrolithiasis and/or ureterolithiasis. This effect is because Indinavir is only soluble in acidic conditions. Additionally, asymptomatic crystalluria has a 66% incidence. The following also increases the risk of lithiasis: Hepatitis B and hepatitis C comorbidities, inadequate hydration, predisposing kidney conditions, and immune deficiencies.
Indinavir is ingested orally, as 100 mg, 200 mg, 333 mg, and 400 mg capsules. The most common indinavir dosage is 800 mg, which is taken as two 400 mg capsules every 8 hours. Recommendations are that patients do not take the medication with food, only water or other liquids (i.e., tea, juice, or coffee). Patients may choose to take indinavir either 1 hour before a meal or two hours after consuming a meal to maximize absorption. If taken with a large meal rich in protein and/or fat, it will diminish the drug's efficacy because of reduced absorption.  However, foods such as bread and milk may be consumed with Indinavir as long as the portions remain small. If a patient misses a dose, the recommendation is that patients take the next dose at the appropriate time interval. Therefore, one should not take multiple doses at the same time.
1. Dual Combination Therapy with Protease Inhibitors (PI)
The following are protease inhibitors used in combination with indinavir. Only one PI would typically be administered concurrently with indinavir. The most common regiment for dual therapy is as follows:
Indinavir (800 mg, orally, every 8 hours) + ritonavir (100 mg to 200 mg, orally, twice a day) Note: take ritonavir with 48 oz of water.
2. Combination Therapy with two Nucleoside Reverse Transcriptase Inhibitors (NRTIs)
Indinavir (800 mg, orally, every 8 hours) + zidovudine (200 mg, orally, every 8 hours) + lamivudine (150 mg, orally, twice a day) reduces HIV RNA levels below 500 copies per milliliter.
Studies suggest that both treatment plans result in similar plasma HIV RNA and CD4+ levels.
If a patient has a diagnosis of hepatic insufficiency before starting treatment, the prescriber should lower the dosage of indinavir to 600 mg. Additionally, if nephrolithiasis or urolithiasis occurs, the medication should be held for 24 to 72 hours or discontinued altogether. Furthermore, patients should consume an average of 1.5 liters or approximately six glasses of 8 fluid ounces of liquid each day to ensure adequate hydration. Remaining hydrated will help with the prevention and severity of both nephrolithiasis and/or urolithiasis.
Optimal dosing remains undetermined for pediatric and pregnant patients. However, indinavir was considered a category C medication under the prior FDA categorization for drugs in pregnancy.
The most common adverse reactions include:
- Nephrolithiasis/urolithiasis: This may occur with symptoms such as flank pain and hematuria, or it may be asymptomatic.
- Renal insufficiency
- Hepatic insufficiency
- Kidney stones, leading to kidney failure
- Kidney inflammation
- Symptomatic hyperbilirubinemia
- Asymptomatic hyperbilirubinemia
- Hyperglycemia, leading to insulin resistance
- Heart attack
- Diabetes, leading to ketoacidosis
- Hemolytic anemia
- Loss or gain of body fat
The most common less serve side effects include:
Some rare side effects include:
- Jaundice (skin or eyes)
Indinavir inhibits CYP3A4, and therefore, medications that also act through this mechanism of action are contraindicated.
- Alpha 1-adrenoreceptor antagonists
- Ergot derivatives
- Sedatives and hypnotics
- Gastrointestinal motility agents
- HMG-CoA reductase inhibitors
- PDE5 inhibitors
Additionally, patients taking phosphodiesterase inhibitors type 5 (PDE5) to treat erectile dysfunction such as sildenafil and tadalafil can cause unwanted side effects such as hypotension and prolonged erections. These side effects may become exacerbated when taken with indinavir.
Patients with a history of kidney stone formation or those at an increased risk of kidney stone development may still be treated with indinavir, although clinicians can consider other alternatives. However, all patients should be closely monitored during the first six months when first starting treatment. Renal function and urinary health require monitoring throughout treatment with indinavir. The majority of stones produced by indinavir are considered radiolucent, and therefore, conventional methods such as CT scans and X-rays of the kidney, ureters, and bladder (KUB) are unable to detect such stones. Therefore, monitoring should occur through a urine analysis capable of detecting crystalluria.
A 2001 review of Indinavir overdoses (n=79) took into account all reports made to the manufacturer of indinavir, Merck & Co. It defined an acute overdose as a single dose of 2400 mg, and a chronic overdose was as recurring doses less than or equal to 2400 mg. The study found that 66% of patients (52/79) experienced an adverse event. It is important to note that the most common reactions for both chronic and acute overdoses were gastrointestinal (nausea, vomiting, abdominal pain) and renal-related (nephrolithiasis/flank pain/renal colic pain).
Common treatment methods for symptomatic Indinavir overdose include hydration (oral or intravenous), diuresis, and activated charcoal to decrease absorption. 87% of patients recovered based on follow-up information provided (n=45). Additionally, an overdose report suggested that 50 mg of activated charcoal was given orally in combination with IV fluids, and the patient was asymptomatic within 4 hours of treatment.
Enhancing Healthcare Team Outcomes
According to indinavir overdose data, it was determined that 70% (46/66) overdoses were accidental. Therefore, all members of the interprofessional healthcare team must communicate clearly to ensure appropriate coordination of care.
To decrease the likelihood that a patient misinterprets dosing instructions or is unable to read or comprehend them, patients must receive adequate counsel by either a pharmacist and/or clinician. Additionally, those responsible for the patient's care should adequately follow up with the patient to ensure that the patient is dosing indinavir correctly, as compliance is essential for effective treatment. Nurses with specialty training in HIV patient care can educate patients and their families about the importance of compliance and side effects. Since ineffective dosing and administration can lead to therapeutic failure, these interprofessional strategies can significantly improve patient outcomes with indinavir therapy. [Level 5]